Hi,
I dove with "Dive with Martin" and it was run pretty good. The boats were smaller and quite quick to get you to the sites, first ones there every day. They pick you up right at the hotel pier and the gear is on the boat and set up, for those of us who rent. The dive guides were knowledgable about the marine life but I had to give the guide crap on the night dive for grabbing the puffer fish by the tail and making it inflate. The price was good also, $200 US for 8 dives plus 1 night dive, all your equipment and an underwater video of one of the dives. Now the video wasn't bad but it wasn't professionally editted either.
I would definetly recommend Cozumel but not the Fiesta Americana.